A liquid crystal display device is a display visualizing polarization by a switching effect of a liquid crystal, and has been used in various categories ranging from small and medium displays, such as a wrist watch, an electronic calculator, and a mobile phone, to a large-scale TV.
Currently, as a considerable number of polarizing plates mass-produced and commercialized for display devices, a matter, which is obtained by joining a protective film which is optically transparent and has a mechanical strength onto both surfaces or one surface of a polarizing film (polarizer) formed by coloring a dichromatic material such as iodine or a dichroic dye on a base film formed of a polyvinyl alcohol-based film, followed by cross-linking by a boron compound and stretching and aligning, has been used.
However, there is a problem in that in a stretched polyvinyl alcohol-based film polarizer, under a durability condition such as a high temperature and a high humidity, shrinkage deformation easily occurs. When the polarizer is deformed, there occur problems in that stress thereof affects the protective film and causes bending, and as a result, a change in physical property of the polarizing plate including the polarizer and a light leakage phenomenon in a liquid crystal display device are caused.
The boron compound generally used in a cross-linking step of a process for manufacturing the polarizer has a short cross-linking chain, and thus, causes significant width shrinkage by a stretching process, and the significant width shrinkage becomes a main reason for shrinkage deformation of the polarizer. In order to solve this, a method for using an organic cross-linking agent in addition to the boron compound, specifically, a method for performing a cross-linking treatment with a polyvalent aldehyde compound has been proposed. However, aldehyde has a peculiar odor and a problem in terms of handling stability. Further, a method for performing a cross-linking treatment with a polyvalent carboxylic acid compound has been proposed, but does not have a sufficient improvement effect of shrinkage deformation of the polarizer.